1. Field of the Invention
This invention is directed to rubber compositions cabable of adhesion to both polymeric and metallic materials. Such composition is useful generally for adhesive bonding of a thermoplastic resin to a metallic material and particularly for firm attachment of a metal fitting to a hose construction. The invention further relates to a method of jointing a coupler on to a hose.
2. Description of the Prior Art
Polymeric materials have of late found application to a wide variety of industrial sectors and household commodities. This trend has lent an impetus to the production of composite polymer materials in which a polymer and a metal are bonded together into an integral structure and further to the development of adhesive compositions for polymer-to-metal bonding.
Prior adhesive compositions are applicable for instance to automotive hoses for air-conditioning and fuel-transporting use. As refrigerants a family of gases known as chlorofluorocarbons (CFCs) have been employed among which dichlorodifluoromethane (CFC 12) is typified. CFC 12, however, is reported to rise into the stratophere and erode the ozone layer that screens out dangerous solar rays and thus induce cutaneous cancer in some cases. The world's industrial nations are required to phase out the use of such ozone-depleting chemical. 1,1,1,2-Tetrafluoroethane (HFC 134a) is considered to be one safe substitute.
An urgent need has arose, in addition to safety examination of HFC 134a by experts, for means ensuring leak proof, maintenance-free transport of that gas as a refrigerant.
Various hoses have been proposed for use in transporting or otherwise handling refrigerants and fuels. One such hose is constructed with a core tube formed from a acrylonitrile-butadiene rubber (NBR) or chlorosulfonated polyethylene (CSM) for its good oil-resistance and refrigerant- and fuel-impermeable properties. To further improve impermeability, another hose has assembled a combination core including an inner peripheral wall of a thermoplastic resin such as a nylon and an outer peripheral wall of a rubbery material such as NBR, CSM or butyl rubber (IIR). Either type of hose is usually provided at each of its opposite ends with an aluminum joint fixed by the use of an adhesive composition for connection to the companion part.
The last-mentioned, laminated-cored hose has a drawback in that on prolonged exposure to a temperature exceeding a working temperature, say from 140.degree. to 160.degree. C., it gets flattened at the inner resinous wall under stresses originating from the joint. In such instances the hose is susceptible to leakage at a lower pressure than a working pressure usually of from 15 to 30 kgf/cm.sup.2 and even at the working temperature. This is evidenced by the following performance tests in which the hose has been examined for air tightness after aging at varying temperatures for different lengths of time.
______________________________________ temperature (.degree.C.) time (hr) pressure (kgf/cm.sup.2) ______________________________________ 120 168 not leaked at 40 140 168 leaked at less than 5 150 168 leaked at less than 5 160 24 leaked at less than 5 ______________________________________
The foregoing hose of a combination core type is wholly unsatisfactory as it is prone to leak only under appreciable stress particularly where it is by sheer accident subject to a higher temperature for a longer period of time. This is literally responsible for laborious maintenance and often for hazardous operation.
The above problems have been coped with by the use of metal joints constituted of a nipple and a socket, the nipple being structured in a trapezoidally channeled, serrated or voluted shape and the socket formed to suit wavy or flat clamping. None of these attempts works to satisfaction from the leakproofness point of view. Alternatively, it is known that a hose body and a metal fitting can be clamped with an O-ring or sleeve interposed therebetween. In this mode of clamping, the packing is objectionably displaceable and difficult to position in place while in interengagement of the hose with the fitting.
To attain integral bonding between a composite hose and a metal joint, it has been proposed that a chlorinated rubber cement be used as an adhesive. This cement tends to adversely affect the resinous material constituting an inner wall of the hose core, rendering the resultant hose assembly sensitive to stress crack and hence fluid leak.